//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
// UNSUPPORTED: c++03, c++11, c++14, c++17

// <span>

// template<size_t Count>
//  constexpr span<element_type, Count> first() const;
//
// constexpr span<element_type, dynamic_extent> first(size_type count) const;
//
// Mandates: Count <= Extent is true.

#include <span>
#include <cassert>
#include <algorithm>
#include <string>

#include "test_macros.h"

template <typename Span, std::size_t Count>
constexpr bool testConstexprSpan(Span sp) {
  LIBCPP_ASSERT((noexcept(sp.template first<Count>())));
  LIBCPP_ASSERT((noexcept(sp.first(Count))));
  auto s1  = sp.template first<Count>();
  auto s2  = sp.first(Count);
  using S1 = decltype(s1);
  using S2 = decltype(s2);
  ASSERT_SAME_TYPE(typename Span::value_type, typename S1::value_type);
  ASSERT_SAME_TYPE(typename Span::value_type, typename S2::value_type);
  static_assert(S1::extent == Count, "");
  static_assert(S2::extent == std::dynamic_extent, "");
  return s1.data() == s2.data() && s1.size() == s2.size() && std::equal(s1.begin(), s1.end(), sp.begin());
}

template <typename Span, std::size_t Count>
void testRuntimeSpan(Span sp) {
  LIBCPP_ASSERT((noexcept(sp.template first<Count>())));
  LIBCPP_ASSERT((noexcept(sp.first(Count))));
  auto s1  = sp.template first<Count>();
  auto s2  = sp.first(Count);
  using S1 = decltype(s1);
  using S2 = decltype(s2);
  ASSERT_SAME_TYPE(typename Span::value_type, typename S1::value_type);
  ASSERT_SAME_TYPE(typename Span::value_type, typename S2::value_type);
  static_assert(S1::extent == Count, "");
  static_assert(S2::extent == std::dynamic_extent, "");
  assert(s1.data() == s2.data());
  assert(s1.size() == s2.size());
  assert(std::equal(s1.begin(), s1.end(), sp.begin()));
}

constexpr int carr1[] = {1, 2, 3, 4};
int arr[]             = {5, 6, 7};
std::string sarr[]    = {"ABC", "DEF", "GHI", "JKL", "MNO"};

int main(int, char**) {
  {
    using Sp = std::span<const int>;
    static_assert(testConstexprSpan<Sp, 0>(Sp{}), "");

    static_assert(testConstexprSpan<Sp, 0>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 1>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 2>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 3>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 4>(Sp{carr1}), "");
  }

  {
    using Sp = std::span<const int, 4>;

    static_assert(testConstexprSpan<Sp, 0>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 1>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 2>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 3>(Sp{carr1}), "");
    static_assert(testConstexprSpan<Sp, 4>(Sp{carr1}), "");
  }

  {
    using Sp = std::span<int>;
    testRuntimeSpan<Sp, 0>(Sp{});

    testRuntimeSpan<Sp, 0>(Sp{arr});
    testRuntimeSpan<Sp, 1>(Sp{arr});
    testRuntimeSpan<Sp, 2>(Sp{arr});
    testRuntimeSpan<Sp, 3>(Sp{arr});
  }

  {
    using Sp = std::span<int, 3>;

    testRuntimeSpan<Sp, 0>(Sp{arr});
    testRuntimeSpan<Sp, 1>(Sp{arr});
    testRuntimeSpan<Sp, 2>(Sp{arr});
    testRuntimeSpan<Sp, 3>(Sp{arr});
  }

  {
    using Sp = std::span<std::string>;
    testConstexprSpan<Sp, 0>(Sp{});

    testRuntimeSpan<Sp, 0>(Sp{sarr});
    testRuntimeSpan<Sp, 1>(Sp{sarr});
    testRuntimeSpan<Sp, 2>(Sp{sarr});
    testRuntimeSpan<Sp, 3>(Sp{sarr});
    testRuntimeSpan<Sp, 4>(Sp{sarr});
    testRuntimeSpan<Sp, 5>(Sp{sarr});
  }

  {
    using Sp = std::span<std::string, 5>;

    testRuntimeSpan<Sp, 0>(Sp{sarr});
    testRuntimeSpan<Sp, 1>(Sp{sarr});
    testRuntimeSpan<Sp, 2>(Sp{sarr});
    testRuntimeSpan<Sp, 3>(Sp{sarr});
    testRuntimeSpan<Sp, 4>(Sp{sarr});
    testRuntimeSpan<Sp, 5>(Sp{sarr});
  }

  return 0;
}
